When a machine tool is used for machining a workpiece, a tool is mounted on a spindle of a spindle device. When the tool is fixed on the spindle, the tool is press-fitted into an attachment seat such as a tapered hole or an end surface that is formed in the spindle. In order to fix the tool to the spindle, it is known that a draw rod, which is referred to as a draw bar, is arranged in the spindle device and draws the tool toward an interior of the spindle so that the tool is fixed to the spindle.
For example, Specification of Japanese Patent No. 3159923 and Japanese Unexamined Patent Publication No. 5-50359A disclose a spindle device in which a draw bar is arranged in a hollow portion of a spindle that is provided rotatably with respect to a housing. The draw bar includes, at a distal end portion thereof, a collet configured to open and close when the draw bar moves in an axial direction. The collet is configured to hold and release a rear end portion of the tool. When the draw bar draws the tool inward in a state in which the collet holds the tool, the tool is fixed to the spindle.